Apparatus for producing corrugations in a hollow body

ABSTRACT

Apparatus for producing in the walls of hollow bodies of revolutions, such as tubes or the like, wavelike corrugations. The apparatus comprises adjacent groups of pressure tools surrounding the body and movable toward the axis thereof to thereby deform with a profiled working end the wall of the body into wavelike corrugations.

United States Patent Arnold et al. 1 1 Apr. 10, 1973 APPARATUS FOR PRODUCING [56] References Cited CORRUGATIONS IN A HOLLOW BODY UNITED STATES PATENTS [75] lnvemms: Hans Arm; Carl-Helm Reich, 441 ,822 12/1890 Browning ..72 402 both of Lage/Lippe, Germany 3,012,604 12/1961 Zieg ....72/402 3,349,600 10/1967 Bijvoet ...72/393 [73] Assgnee- Reche age/W9 Germany 3,439,521 4/1969 Tetart ...72/385 22 Filed: May 27 1971 3,472,418 10/1969 Ullman ..72/393 [21] Appl. No.: 147,464 Primary Examiner-Richard J. Herbst Assistant Examiner-Gene P. Crosby A Foreign Application Priority Data tzorney M1chael S Striker June 5, 1970 Germany ..P 20 27 638.4 ABSTRACT Apparatus for producing in the walls of hollow bodies [52] US. Cl. ..72/402, 72/403, 72/404 of revolutions, such as tubes or the like, wavelike c0!- [51] Int. Cl. ..B21d 15/00 rugations. The apparatus comprises adjacent groups of [58] Field of Search ..72/402, 403, 404, pressure tools surrounding the body and movable toward the axis thereof to thereby deform with a profiled working end the wall of the body into wavelike corrugations.

12 Claims, 9 Drawing Figures i i 1 JL r i l. 1 .i 1 1 1 I I 12 6 5 4 a PATEL 1 [0 APR 1 [H973 SHEET 3 [IF 4 I I I I I I I I I I I I I I I I I I I I I I I u I I I I I I I I I I n I I u I I I n l I I I l I I r I I I I n I if w 1 .r. f MW Q M NJ m Md 4. A HMH am a APPARATUS FOR PRODUCING CORRUGATIONS IN A HOLLOW BODY BACKGROUND OF THE INVENTION groups of pressure tools surrounding the body or tube to be deformed and in which the pressure tools are moved in longitudinal direction toward the axis of the tube to thereby deform the tube wall into wavelike corrugations.

Apparatus of this type is known in the art, but in the apparatus known in the art, the wavelike corrugations formed in the tube wall have uniform profiles and the same wall thickness and hardness throughout the length of the tube so that such corrugated tubes have throughout their lengths a predetermined and uniform resistance against compression in axial direction.

Such tubes produced with apparatus known in the art have also been used in frames of automotive and similar vehicles, but such corrugated tubes are not best suitable for certain purposes in such constructions. For safety reasons, there are provided in such constructions, especially in front of spaces which should be protected in case of collision, compressible zones which have a smaller resistance against compression in axial direction than the remainder of the frame construction. Corrugated tubes which have throughout their lengths a uniform resistance against compression in axial direction are, however, not best suited for this purpose, since such tubes will buckle midway between their fixed ends if excessively compressed in axial direction, resulting thereby in a sudden collapse over their whole length.

SUMMARY OF THE INVENTION It is an object of the present invention to provide for an apparatus of the aforementioned kind for producing in the walls of hollow bodies of revolution, especially tubes and the like, wavelike corrugations in which the apparatus is constructed in such a manner that it is possible to produce therewith in a single operation in hollow bodies of revolutions axially spaced zones of different resistance against compression in axial direction.

It is a further object of the present invention to provide for such an apparatus which is simple in construction and operation and which will stand up perfectly under extended use.

It is a further object of the present invention to provide for a hollow body of revolution with walls deformed into wavelike corrugations and in which the hollow body of revolution, especially a tube, has axially spaced zones of different resistance against compression in axial direction.

In accordance with the objects of the present invention, the apparatus of the present invention for producing in the walls of hollow bodies of revolutions, such as tubes or the like, wavelike corrugations, and in which each body is provided with at least one annular zone having a greater resistance against axial compression than the remainder of the body, mainly comprises a mandrel insertable into the hollow body and having an outer surface provided with corrugations substantially corresponding to the corrugations to be formed in the wall of the body, a plurality of axially displaced, adjacent groups of elongated pressure tools surrounding the body and each having a working end facing the body and provided with a profile having in axial direction a contour substantially corresponding to that of a corrugation to be formed and each movable along a working stroke in longitudinal direction between a retracted, inoperative position and an advanced, active position in which the working ends of the tools cooperate with the mandrel to deform the wall of the hollow body or tube into finished corrugations. The tools in each group are arranged so that the working ends in their advanced end positions form a complete circle about the body. The apparatus includes further means for moving each group of tools successively from the retracted toward the advanced end position in such a manner that in the zones of the body to be provided with a greater resistance against compression in axial direction movement of at least one group of tools from said retracted to said advanced position is started before the preceding group of tools has reached its advanced end position while in the remaining zones of the body, movement of each group of tools from the retracted to the advanced position is started only after the preceding group of tools has reached its advanced end position.

In a special simple construction according to the present invention, the moving means comprise a pressure ring movable along an active stroke in axial direction and being provided with control faces arranged for cooperation with the ends of the tools opposite the working ends thereof, and the control faces of the pressure ring are inclined to the direction of movement of the pressure ring along the active stroke in such a manner that the leading ends of said faces are spaced further from the axis of the ring than the trailing ends thereof.

When now two consecutive groups of tools are during part of their inward stroke simultaneously operated by the control faces of the pressure ring in such a manner that the movement of one group of tools leads the movement of the other group of tools, then the flow of the material of the tube walls into the working region of the preceding group of tools, will be interrupted at the moment of engagement of the trailing group of tools with the surface of the tube wall. Therefore, the necessary material for forming the corrugation by the trailing group of tools will be taken out of the wall thickness of the tube wall and this will result in a cold work-hardening of the tube portions engaged by the trailing group of tools whereby the resistance of this corrugation against compression in axial direction will be increased.

The zones with smaller resistance against compression in axial direction are obtained in that the control faces of the pressure ring will act in such zones at any given moment only on a single group of tools located in a plane substantially normal to the tube axis so that during deformation of the tube wall into corrugation by a single group of tools, the material may flow to opposite sides of this group of tools so that no additional cold work-hardening will occur.

In order to increase the difference against axial compression in various zones of the tubes, it is alsopossible to arrange the control faces of the pressure ring and the cooperating ends of the groups of tools in such a manner that some group of tools will have a different active stroke in radial direction of the tube than the other groups of tools, so that corrugations of different depths may be formed. It is also possible to provide adjacent groups of tools at the working ends with different profiles to thereby also influence the resistance of successive zones of the corrugated tube against axial compression.

The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a plan view, partly in section, showing the general arrangement of the apparatus according to the present invention;

FIG. 2 is a cross-section taken along the line II-II of FIG. 1;

FIG. 3 is a partial schematic view in longitudinal section and illustrating in part one of the embodiments according to the present invention;

FIG. 4 is a partial sectional view of a second embodiment according to the present invention;

FIG. 5 is a partial longitudinal section of a third embodiment according to the present invention;

FIG. 6 is a top view of the tools as shown in FIG. 5, as viewed in the direction of the arrow VI;

FIG. 7 is a bottom view of the tools as shown in FIG. 5, as viewed in the direction of the arrow VII;

FIG. 8 is a partial view of showing a modification in which adjacent groups of tools are provided with different profiles at their working ends; and

FIG. 9 is a partial view of a further modification in which the tools and the pressure ring are arranged with respect to each other to produce in adjacent groups of tools different working strokes of the tools in longitudinal direction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically illustrates the overall arrangement of the apparatus according to the present invention. As can be seen from FIG. 1, the apparatus comprises a mandrel 2 provided on the peripheral surface thereof with wavelike corrugations 3, which substantially correspond to the corrugations to be formed in the tube 1, the wall of which is to be deformed into wavelike corrugations with the apparatus of the present invention. The mandrel 2 which is inserted into the tube to be deformed is constructed in a known manner, not forming part of the present invention, as a collapsible mandrel so that after forming the corrugations in the tube, the mandrel may be collapsed and withdrawn from the corrugated tube. The tube 1 is surrounded by a substantially cylindrical housing 4 provided with a plurality of circumferentially spaced axially elongated and radially extending slots 4a therethrough, in which rows of elongated pressure tools 5 are mounted movable in radial direction between an outer, retracted inactive position and an inner, radially advanced active position. Each of the tools 5 has at its inner end a profile corresponding substantially to the outer profile of the corrugations to be formed in the tube.

In the embodiment as illustrated in FIGS. 1 and 2, there are eight pressure tools 5 in each group arranged in a plane normal to the axis of the tube and surrounding the tube in such a manner that in the advanced working position of the tools, the working ends of the tools in the advanced end position thereof, form a complete circle as shown in FIG. 2. The tools of the plurality of groups are arranged in the slots 4a of the housing 4 so that they abut in axial direction of the housing against each other.

By selection of the profile of the working ends 6 of the pressure tools, it is possible to influence or to change the profile of the corrugations to be formed in the tube 1 from one corrugation into the next, or for a group of corrugations.

The pressure tools 5 are preferably moved from their retracted inactive position to their advanced active position by means of a pressure ring 8 which is arranged coaxially with the axis 7 of the tube, and which is moved during its working stroke in the direction of the arrow 9 along this axis. The pressure ring 8 is provided at its lower end and at the inner surface thereof with a conical control face 10 which tapers in the direction opposite to the direction of the movement of the ring during its working stroke.

The conical control face 10 of the pressure ring cooperates with the outer'end faces 11 of the pressure tools. Each of the tools 5 is provided intermediate its ends with an axially extending opening therethrough of substantially rectangular configuration and a rod 13 extends through each of the axially aligned openings of the rows of tools respectively located in the slots 40 of the housing 4. Each of the rods 13 has a pair of portions extending in the axial direction of the pressure ring and a connecting portion 14 connecting the aforementioned parallel portion and extending outwardly inclined to this axial direction. The transverse length of the connecting portion corresponds substantially to the radial movement of the pressure tools between the retracted and the advanced position thereof. In the arrangement as shown in FIG. 1, the various rods 13 are connected with the pressure ring 8 for movement in axial direction by means of an outer housing 35 in which the pressure ring is mounted and a cover 36 connected to the cylindrical wall of the outer housing 35.

As shown in FIG. 1, the connecting portion 14 trails in the direction of movement of the pressure ring 8 along its active stroke the trailing end of the control face 10. During movement of the pressure ring 8 in the direction as indicated by the arrow 9, each of the pressure tools 5 is first moved from its retracted inactive position to its advanced active position, and subsequently thereto, each of the tools is moved by the cooperation of the connecting'portion 14 of the rods with the outer faces of the openings 12 in each pressure tool again in radially outward direction from its advanced position to its retracted inactive position. The rods 13 therefore form retracting means for retracting the tools from their advanced active position to their retracted inactive position, in which the working ends of the tools are retracted from the corrugations formed in the tube.

FIGS. 1 and 2 illustrate only the general arrangement of the apparatus according to the present invention, whereas the specific arrangements of the present invention for producing in the tube 1 corrugated zones of different resistance against axial compression are illustrated in the FIGS. 3-9.

In the embodiment shown in FIG. 3 only part of the pressure tools are illustrated and the pressure ring 8 cooperating therewith, while the other elements of the apparatus, as described in connection with FIGS. 1 and 2, are for simplification reasons omitted from this Figure. In the embodiment as shown in FIG. 3, the groups of pressure tools 16-19 are constructed and arranged to provide during their cooperation with the control face 10 of the pressure ring 8 in the tube 1 corrugations which have a higher resistance against compression in axial direction than the corrugation produced by the adjacent groups of tools 21 and 22. As shown in FIG. 3, the conical control face 10 of the pressure ring 8 extends in axial direction of the pressure ring for a distance a and the groups of pressure tools 16-19 have at their inner or profiled working ends, a thickness in axial direction b, which is equal to the dimension a, whereas the outer ends of the aforementioned groups of tools have in axial direction a thickness c, which is smaller, for instance half of the distance of a. The groups of tools 16-19 are offset intermediate their ends, as shown in FIG. 3, to an extent which increases in direction of the working stroke, indicated by the arrow 9, of the pressure ring.

The specific arrangement of the pressure tool groups 16-19 as shown in FIG. 3 will assure that during the movement of the pressure ring along its working stroke in the direction of the arrow 9, two groups of pressure tools from the groups 16-19, during part of their inward stroke, will be simultaneously operated whereby one of the group precedes the movement of the other group.

If the pressure ring 8 in the embodiment shown in FIG. 3 is moved towards the left, as viewed in this Figure, then the tools of the group of tools 16 will first be moved from the retracted position as shown in FIG. 3, to their advanced position so that the profiled inner working end of the tools 16 will deform the wall of the tube 1 to a corrugation and, before the outer ends of the tools 16 reach the trailing end 10' of the control face 10, the outer ends of the tools 17 of the following group will come into contact with the leading end 10" of the control face so that the tools of the group 17 will also be moved inwardly before the pressure tools 16 have finished their working stroke. As the tools of the group 17 move to their advanced position flow of the material of the tube wall in the region engaged by the working ends of the tools 16 in axial direction will be interrupted so that the working ends of the tools 16 will carry out an increased cold work-hardening of the engaged tube portion to thereby increase the resistance of the thus formed corrugation against compression in axial direction. Before the group of tools 17 have finished their deformation of the corresponding portion of the tube wall, the group of pressure tools 18 are also brought into engagement with the tube 1 so that the same cold work-hardening will again be produced.

Thus, in the zone of the corrugations produced by the groups of pressure tools 16-19, there will occur a cold work-hardening of the corresponding tube wall portions so that in this zone an increased resistance against compression in axial direction will be produced.

Due to the stepwise interengagement of the pressure tools 16-19, as shown in FIG. 3, there is provided to the left of the outer end of the tools 19 an annular groove 20 open towards the control face 10, so that during movement of the control face 10 through this groove 20, no radial movement of the pressure tools will occur.

The following groups of tools 21 and 22 have through their full length a uniform thickness b in axial direction which is equal to the dimension a. The pressure tools of the groups of pressure tools 21 and 22 will therefore be radially moved one after the other. The deformation work of the group of tools 22 will begin only after the deformation work of the group of pressure tools 21 has been finished. During such deformations, there will evidently not occur an increased cold work-hardening and therefore there will be produced a zone in the tube which has a smaller resistance against axial compression than the zone of corrugations produced by the pressure tools 16-19.

FIG. 4 illustrates a second embodiment according to the present invention. In the embodiment shown in FIG. 4, each of the pressure tools is provided with a nose portion 23 extending transverse to the elongation of the respective tool, and extending into a cut-out 24 or 25 of the following tool. Each of the nose portions 23 has a face 23' extending transverse and preferably normal to the direction of elongation of the respective tool and facing a substantially parallel face 24', respectively 25 of the cut-out formed in the following tool. The spacing c between the faces 23 and 24 in the group of tools 26 encompassing the zone e, is smaller than the distance h, i.e., the radial extension of the control face 10, so that during movement of the pressure ring in the direction of the arrow 9, there will always be two adjacent groups of pressure tools 26 in the zone e, during part of their inward stroke, which will be moved simultaneously, while advance of one group of pressure tools 26 will precede the advance of the following group of pressure tools within the zone e. In this way, the group of tools 26 will produce in the region of the zone e the above-described cold work-hardening of the corresponding tube portions which will result in this zone to an increased resistance of the corrugations against compression in axial direction.

In the region f, the faces 23 and 25 of the pressure tool 27 are spaced a distance d from each other when the pressure tools are in their retracted position, and this distance d is equal to the radial distance h of the control face 10 of the pressure ring.

In the region f, the pressure tools are therefore arranged in such a manner that they will be moved radially inwardly by the control face 10 one after the other, so that one group of pressure tools 27 will start to move inwardly only after the preceding group of pressure tools 27 have already finished their working stroke so that no increased work-hardening will occur.

FIGS. 5-7 illustrate a further embodiment according I to the present invention. As shown in FIG. 5, the pressure ring is provided in this embodiment for each row of pressure tools 31 with two different control faces 29 and 30. The active portion of the control face 29 extends in axial direction of the pressure ring 28 for a distance a1, whereas the control face 30 extends in axial direction for a distance a2.

In the region of the pressure tools 31, which are arranged to produce in the tube i corrugations having a higher resistance against compression in axial direction, the radial inward movement of the pressure tool 31 is enforced by the control faces 29. The thickness b in axial direction of the pressure tool 31 is smaller than the axial length al of the control faces 29, so that in the region of the pressure tools 31, always two groups of adjacent pressure tools will be simultaneously operated, during part of their inward stroke, whereby one group of pressure tools precedes the movement of the other group of pressure tools. This will result in an increased work-hardening of the tool portions engaged by the profiled working ends of the pressure tools 31. The control faces 29 are formed by bottom faces of grooves respectively aligned with the row of pressure tools, whereas the control face 30 can be formed as an uninterrupted frustoconical face. The control faces 29 cooperate with the surfaces 32 of the pressure tool 31 shown in FIG. 6, and in order to prevent engagement of the outer ends of the pressure tools 31 with the frustoconical control face 30, the outer ends of the pressure tools 31 are provided with cut-outs 33 as shown in FIG. 6.

The frustoconical control face 30 will thus cooperate only with the outer ends of the groups of pressure tool 34 which follow the group of pressure tools 31. The axial thickness of the pressure tools 34 is equal to the axial length a2 of the control face 30 so that the pressure tools 34 of adjacent groups of these pressure tools will be moved one after the other in radial inward direction towards the tube 1. An increased cold workhardening of the corresponding tube portions will therefore not be produced by the pressure tools 34 so that these pressure tools will produce corrugations in the tube which have a smaller resistance against axial compression than the corrugations produced by the pressure tools 31.

It is also possible to influence the resistance of the corrugations against compression in axial direction by forming the working ends of adjacent groups of tools or in a plurality of groups of tools with slightly different profiles, and such an arrangement is shown in FIG. 8 in which the profile 37' of the tool 37 differs from the profile 38' of the adjacent tool 38.

It is also possible to make the length of the working tools of adjacent groups or of a plurality of adjacent groups slightly different from each other, as shown in FIG. 9 in which the overall length of the working tool 39 is slightly greater by a distance g than that of the adjacent pressure tool 40 so that the radial stroke produced by the control face on the pressure tool 39 will be greater than that of the pressure tool 40.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of apparatus for manufacturing tubes with wavelike corrugated walls differing from the types described above.

While the invention has been illustrated and described as embodied in apparatus for manufacturing tubes with wavelike corrugated walls having axially spaced zones of different resistance against compression in axial direction, it is not intended to be limited to the details shown, since various modifications and structural changes made be made without departing in any way from the spirit of the present invention.

For instance, while in FIGS. 3, 4 and 5 the control faces are integral with the pressure ring, it is also possible to provide these control faces on separate inserts in the pressure ring which can be exchanged after wear. Furthermore, while the control faces have been shown and described as plane or conical faces with straight generatrices, it is also possible to give these control faces a different configuration and thereby control the movement of the pressure tools.

Also, in order to reduce the specific pressure between the control faces and the outer ends of the pressure tools, it is advantageous to provide the outer ends of the pressure tools with faces inclined in the same direction as the control faces so as to assure full surface contact between these faces, as for instance shown in FIG. 1 of the drawing.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can be applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by letters patent is set forth in the appended.

We claim:

1. Apparatus for producing in the walls of hollow bodies of revolutions, such as tubes or the like, wavelike corrugations in which each body is provided with at least one annular zone having a greater resistance against axial compression than the remainder of said body, said apparatus comprising, a mandrel insertable into the hollow body and having an outer surface provided with corrugations substantially corresponding to the corrugations to be formed in the wall of the body; a plurality of axially displaced, adjacent groups of elongated pressure toolssurrounding the body and having each a working end facing the body and provided with a profile having in axial direction a contour substantially corresponding to that of a corrugation to be formed and each movable in longitudinal direction between a retracted inoperative position and an advanced active end position in which the working ends of the tools cooperate with said mandrel to deform said wall into finished corrugations, the tools in each group being arranged so that said working ends in their advanced end positions form a complete circle about the body; and means for moving each group of tools successively from said retracted toward said advanced end position in such a manner that in the zones of said body to be provided with a greater resistance against compression in axial direction movement of at least one group of tools from said retracted to said advanced position is started before the preceding group of tools hasreached its advanced end position, while in the remaining zones of said body movement of each group of tools from said retracted to said advanced position is started only after the preceding group of tools has reached its advanced end position.

2. An apparatus as defined in claim 1, wherein said moving means comprise a pressure ring movable along an active stroke in axial direction and being provided with control faces arranged for cooperation with the ends of said tools opposite the working ends thereof, said control faces being inclined to the direction of movement of said pressure ring along said active stroke in such a manner that the leading ends of said faces are spaced further from the axis of the ring than the trailing ends thereof.

3. An apparatus as defined in claim 2, wherein said control faces extend in axial direction of the ring for a predetermined distance, and wherein all tools have at portions thereof facing the ring axis, a thickness in the direction of the ring axis equal to said predetermined distance and wherein the opposite ends of the tools for producing said zones of greater resistance against compression in axial direction have-in said axial direction a thickness smaller than said predetermined distance.

4. An apparatus as defined in claim 3, wherein said opposite ends of said tools for producing said zones of greater resistance against axial compression have a thickness substantially half of said predetermined distance.

5. An apparatus as defined in claim 3, wherein the tools of groups of tools for producing the zone of higher resistance against compression in axial direction are offset between the ends thereof to an extent increasing in the direction of movement of the pressure ring from one to the next of said group of tools to form between the trailing group of the aforementioned groups of tools and the following group an annular groove facing said control faces.

6. An apparatus as defined in claim 2, wherein each of said pressure tools has a nose portion extending transverse to its elongation and extending into a cut-out of the following tool, each of said nose portions having a face facing a face of the corresponding cut-out and spaced therefrom in said retracted position of said tools, the spacing of said faces of the groups of tools for producing a zone of greater resistance against compression in axial direction being smaller than the stroke of said tools during their movement from said retracted to said advanced end positions whereas the spacing of said faces of the groups of tools for producing a zone of smaller resistance against axial compression are substantially equal to said stroke.

7. An apparatus as defined in claim 2, wherein the tools in each group of tools are respectively aligned in axially extending rows with the tools in the adjacent groups and wherein said pressure ring has at least two different control faces coordinated with each of said rows of tools, one of said control faces being arranged to cooperate with the opposite ends of the tools arranged to produce a zone of greater resistance against compression in axial direction and the other of said control faces being arranged to cooperate with the opposite ends of the tools arranged to produce a zone of smaller resistance against compression in axial direction, said one control face extending in axial direction of the pressure ring for a distance greater than the thickness of the first-mentioned group of pressure tools in axial direction and the other of the control faces extends in axial direction a distance substantially equal to the thickness of the second-mentioned group of pressure tools.

8. An apparatus as defined in claim 1, and including means cooperating with said tools for retracting the same from said advanced to said retracted position.

9. An apparatus as defined in claim 1, wherein said tools in each group of tools are respectively aligned in axially extending rows with the tools of the adjacent groups, and wherein the tools of each row are formed with axially aligned openings, and including retracting means for retracting said tools from said advanced to said retracted position, said retracting means comprising a plurality of rods connected to said moving means for movement in axial direction and each having a pair of parallel portions extending in said axial direction and a connecting portion connecting said parallel portions and extending outwardly inclined to said axial direction, said rods extending respectively through said opening in said row of tools.

10. An apparatus as defined in claim 1, wherein the profiles at the working ends of the tools in adjacent groups of tools differ from each other.

11. An apparatus as defined in claim 1, wherein said moving means and said groups of tools are arranged with respect to each other so that the tools in at least some groups of tools are moved in longitudinal direction a distance differing from the movement of the other groups of tools.

12. An apparatus as defined in claim 9, wherein said moving means comprise a pressure ring movable along an active stroke in axial direction and provided with control faces arranged for cooperation with the ends of said tools opposite the working ends thereof, said control faces being inclined to the direction of movement of said pressure ring along said active stroke in such a manner that the leading ends of said faces are spaced further from the axis of the ring than the trailing ends thereof, wherein said connecting portion of said rods tails said trailing ends of said control faces in the direction of movement of said pressure ring along said active stroke. 

1. Apparatus for producing in the walls of hollow bodies of revolutions, such as tubes or the like, wavelike corrugations in which each body is provided with at least one annular zone having a greater resistance against axial compression than the remainder of said body, said apparatus comprising, a mandrel insertable into the hollow body and having an outer surface provided with corrugations substantially corresponding to the corrugations to be formed in the wall of the body; a plurality of axially displaced, adjacent groups of elongated pressure tools surrounding the body and having each a working end facing the body and provided with a profile having in axial direction a contour substantially corresponding to that of a corrugation to be formed and each movable in longitudinal direction between a retracted inoperative position and an advanced active end position in which the working ends of the tools cooperate with said mandrel to deform said wall into finished corrugations, the tools in each group being arranged so that said working ends in their advanced end positions form a complete circle about the body; and means for moving each group of tools successively from said retracted toward said advanced end position in such a manner that in the zones of said body to be provided with a greater resistance against compression in axial direction movement of at least one group of tools from said retracted to said advanced position is started before the preceding group of tools has reached its advanced end position, while in the remaining zones of said body movement of each group of tools from said retracted to said advanced position is started only after the preceding group of tools has reached its advanced end position.
 2. An apparatus as defined in claim 1, wherein said moving means comprise a pressure ring movable along an active stroke in axial direction and being provided with control faces arranged for cooperation with the ends of said tools opposite the working ends thereof, said control faces being inclined to the direction of movement of said pressure ring along said active stroke in such a manner that the leading ends of said faces are spaced further from the axis of the ring than the trailing ends thereof.
 3. An apparatus as defined in claim 2, wherein said control faces extend in axial direction of the ring for a predetermined distance, and wherein all tools have at portions thereof facing the ring axis, a thickness in the direction of the ring axis equal to said predetermined distance and wherein the opposite ends of the tools for producing said zones of greater resistance against compression in axial direction have in said axial direction a thickness smaller than said predetermined distance.
 4. An apparatus as defined in claim 3, wherein said opposite ends of said tools for producing said zones of greater resistance against axial compression have a thickness substantially half of said predetermined distance.
 5. An apparatus as defined in claim 3, wherein the tools of groups of tools for producing the zone of higher resistance against compression in axial direction are offset between the ends thereof to an extent increasing in the direction of movement of the pressure ring from one to the next of said group of tools to form between the trailing group of the aforementioned groups of tools and the following group an annular groove facing said control faces.
 6. An apparatus as defined in claim 2, wherein each of said pressure tools has a nose portion extending transverse to its elongation and extending into a cut-out of the following tool, each of said nose portions having a face facing a face of the corresponding cut-out and spaced therefrom in said retracted position of said tools, the spacing of said faces of the groups of tools for producing a zone of greater resistance against compression in axial direction being smaller than the stroke of said tools during their movement from said retracted to said advanced end positions whereas the spacing of said faces of the groups of tools for producing a zone of smaller resistance against axial compression are substantially equal to said stroke.
 7. An apparatus as defined in claim 2, wherein the tools in each group of tools are respectively aligned in axially extending rows with the tools in the adjacent groups and wherein said pressure ring has at least two different control faces coordinated with each of said rows of tools, one of said control faces being arranged to cooperate with the opposite ends of the tools arranged to produce a zone of greater resistance against compression in axial direction and the other of said control faces being arranged to cooperate with the opposite ends of the tools arranged to produce a zone of smaller resistance against compression in axial direction, said one control face extending in axial direction of the pressure ring for a distance greater than the thickness of the first-mentioned group of pressure tools in axial direction and the other of the control faces extends in axial direction a distance substantially equal to the thickness of the second-mentioned group of pressure tools.
 8. An apparatus as defined in claim 1, and including means cooperating with said tools for retracting the same from said advanced to said retracted position.
 9. An apparatus as defined in claim 1, wherein said tools in each group of tools are respectively aligned in axially extending rows with the tools of the adjacent groups, and wherein the tools of each row are formed with axially aligned openings, and including retracting means for retracting said tools from said advanced to said retracted position, said retracting means comprising a plurality of rods connected to said moving means for movement in axial direction and eacH having a pair of parallel portions extending in said axial direction and a connecting portion connecting said parallel portions and extending outwardly inclined to said axial direction, said rods extending respectively through said opening in said row of tools.
 10. An apparatus as defined in claim 1, wherein the profiles at the working ends of the tools in adjacent groups of tools differ from each other.
 11. An apparatus as defined in claim 1, wherein said moving means and said groups of tools are arranged with respect to each other so that the tools in at least some groups of tools are moved in longitudinal direction a distance differing from the movement of the other groups of tools.
 12. An apparatus as defined in claim 9, wherein said moving means comprise a pressure ring movable along an active stroke in axial direction and provided with control faces arranged for cooperation with the ends of said tools opposite the working ends thereof, said control faces being inclined to the direction of movement of said pressure ring along said active stroke in such a manner that the leading ends of said faces are spaced further from the axis of the ring than the trailing ends thereof, wherein said connecting portion of said rods tails said trailing ends of said control faces in the direction of movement of said pressure ring along said active stroke. 